Light emitting diodes or solid-state lighting are replacing incandescent bulbs, compact fluorescent lamp (CFL), High Pressure Sodium Vapor Lamp, Metal Halide Lamp and Halogens as a source of illumination for various indoor and outdoor applications worldwide. According to a study, by U.S. Department of Energy published in Pittsburgh LED Street Light Research Project, use of LED (light-emitting diodes) lighting can reduce energy consumption by one-quarter, saving $120 billion in energy costs and diverting 246 million metric tons of carbon emissions in US alone.
However, management of the performance and life of LEDs is the major hurdle for successful and economical implementation of LED/SSL based lighting fixtures. Life and performance of any LED/SSL based device is critically associated with the heat generated during the operation of the LED. According to a study published in Pittsburgh LED Street Light Research Project it is estimated that about 70% to 80% of power consumed is converted to heat and only 20% to 30% is converted to visible light. Another paper published by authors N. Naredranet. al., having title“Long-term performance of White LED's and systems” discloses that the drive current and the ambient temperature surrounding the LED also affect the performance of LED device. Thus, making the use of the LED lighting systems, more apt for colder regions where the ambient temperature of the surrounding is lower, helping LED to perform better and have a higher rated life.
Moreover, the performance of LED lighting systems is affected by high operating temperatures. The high operating temperature degrades the performance of the LED lighting systems and also hampers the rated life. Empirical data has shown that LED lighting systems may have lifetimes up to50,000 hours while at room temperature; however, operation at close to 90 degree Celsius may reduce the LED life to less than 7,000 hours. Thus, effective management of the heat generated by the LEDs is critical technical problem.
Another factor affecting the successful and commercial implementation of the LEDs is the cost of the LED based lighting systems. The cost for LED based lighting system has two major components, the cost of LEDs, and the cost of material used as Heat Sink. With the pace at which the research is being made on LEDs and their manufacturing process, it is evident that the manufacturing cost for LEDs would reduce drastically over the time. Thereby, the quantum of metal used as heat sink would govern the affordability for a LED/SSL based lighting system. The amount of material used (especially cost of metal) shall dominate the cost of entire lighting apparatus.
Thus, the effective dissipation of heat for per gram of metal used to prepare a lighting fixture remains a long felt need of the society.
One of the prior art known to us that addresses the problem related to heat management in LED based lighting apparatus is discussed below:
US 2008007953 application filed by Keller Berndet. al. discusses the issue of heat management for solid-state lighting to improve the life and performance. The disclosure teaches the use of heat sink having at least partially porous structure. Keller Bernd et. al. further teaches that the pores in the material should interconnect with each other to facilitate an effective convective heat exchange with the ambient air.